I have a 75 bus, and just replaced the muffler with an after market muffler I ordered at CIP1 called "the eliminator style".

Aside from being a bit noisier than my previous muffler (which was a GT 4 tip sports muffler), I noticed that when ever I let up on the accelerator (decel) or come down a hill in a lower gear (pulling lots of vaccum), I now get alot of "popping" in the exhaust.

Usually this is due to an air leak in the headers some where, or a bad exhaust gasket, but I was just wondering if this "eliminator" style of muffler tends to cause such noises, and whether it is normal for these types of mufflers?


By the way, my bus tends to eat up mufflers about once a year. I was hoping this new brand would last a bit longer.
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I would have to ask if there was an EGR take off on the muffler and if it was hooked up to a solid EGR filter or properly blocked off as to not cause an exhaust leak. Then I would check the triangle flanges and make sure they are sealing properly. Most heater box flanges on the 75-78s are usually thinned by corrosion and warped making a proper seal hard to maintain. I use hi temp orange silicone to seal these joints and it always works well (I hate exhaust leaks). Of course if the heater box flanges are warped you can sometimes massage them with a hammer until they are more seal-able but if too far gone may need to be replaced. A last suggestion if the exhaust flows better than the last the idle mixture may need adjusting as during decel it may be leaning out and getting a lean pop out the exhaust but all other areas should be looked at first.

I don't know if this helps but my 2 cents worth,
Gary - CIP1.com. 


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